The present invention relates to a screen printing apparatus for printing cream solder, conductive paste or the like paste on a substrate, and a screen printing method.
Screen-printing is a popular process for printing cream solder, conductive paste or the like paste on the surface of a substrate used when mounting electronic components on the substrate. A screen mask provided with pattern holes in areas corresponding to the target region of printing is placed on a substrate making contact with the surface, a paste is supplied on the screen mask to be squeezed by a moving squeegee, and the paste infiltrating through the pattern holes is printed on the substrate.
In order to provide a superior printing quality, viscosity of the paste needs to be maintained at an appropriate level during the printing operation. For this purpose, a temperature control mechanism is provided in the screen printing apparatus for keeping the temperature of the paste dispensed on a mask plate within a certain range. A temperature control mechanism employed in conventional screen printing apparatus is configured to have an air blowing mouth above a squeegee which moves sliding on a mask plate; the temperature-conditioning air is blown from the mouth towards the surface of the mask plate.
However, in the above described temperature control mechanism, smooth flow of the temperature-conditioning air delivered from the air blowing mouth is disturbed every time when a squeegee holding head, which is locating in between the air blowing mouth and the mask plate, moves for squeezing the paste. This hinders the temperature control mechanism from performing at full function and the operational efficiency is deteriorated. If a massive airflow is provided on the mask plate in order to raise the temperature control function to a satisfactory level, the paste is deprived too much of volatile matters contained therein and the paste becomes dried.
The present invention addresses the above described drawbacks and aims to offer a screen printing apparatus, as well as a screen printing method, in which the temperature of paste can be controlled efficiently using a limited quantity of blowing air, and superior printing quality is assured.
A screen printing apparatus of the present invention comprises a substrate holding section for holding a substrate, a squeegee which slides on a mask plate having a pattern hole for printing a paste dispensed on the mask plate and filtrated through the pattern hole on the substrate, and an air blower for blowing the temperature-conditioning air sidewise towards paste disposed on the mask plate. In the above described configuration, since temperature-conditioned air is blown toward the paste from the side, the air flow is not disturbed by a squeegee unit; so, a small amount of air can efficiently control the temperature of the paste.
It is preferred to provide the air blower with an air blowing slit for forming an air curtain, in order to curtail the thermal convection outwardly from a the space containing an object of the temperature control to the outside environment. The air curtain contributes to further reduce the volume of the temperature-conditioning air needed to keep the paste on the mask plate at a specified temperature level.
A screen printing method of the present invention comprises the steps of placing a mask plate having a pattern hole on a substrate to make contact on the surface, dispensing paste on the mask plate, moving a squeegee to slide on the mask plate so that the paste filtrating though the pattern hole is printed on the substrate, and blowing the temperature-conditioning air sidewise towards the paste for keeping the paste disposed on the mask plate at a specified temperature level.
It is preferred in the above printing method to form an air curtain for curtailing the air convection outwardly from a space containing an object of temperature control to the outside environment.